Electric utility companies and power consuming industries have in the past employed a variety of approaches to metering electrical energy. Typically, a metering system monitors power lines through isolation and scaling components to derive polyphase input representations of voltage and current. These basic inputs are then selectively treated to determine the particular type of electrical energy being metered. Because electrical uses can vary significantly, electric utility companies have requirements for meters configured to analyze several different nominal primary voltages, the most common of which are 96, 120, 208, 240, 277 and 480 volts RMS.
Electric utility meters employing electronic components instead of electromechanical components have become more widely used in the industry. The use of electronic components including microprocessor components have made electricity metering faster and more accurate. Unlike the former electromechanical components, however, the electronic components in the meter require power to operate. Usually, direct current (DC) power is required to operate the meter's electronic components. Of course, the meters typically receive and monitor alternating current (AC) power from the power distribution system. Therefore, electronic meters use power supply devices to generate DC power from the already-available and constantly-present line voltage. As discussed in U.S. Pat. No. 5,457,621, which is incorporated herein by reference, power supply devices have been created to generate the required microprocessor DC power regardless of the value of the available line voltages (e.g., 96 to 480 volts RMS).
Even with the shift away from electromechanical meters to electronic meters, the cost of the product is a meaningful consideration. The power supply component for the electronic meter typically represents a significant portion of the overall cost of the meter. In addition, the power supply's cost is dependent largely on the amount of power consumed by the electronic components in the meter. Therefore, reducing the cost of the meter involves considering techniques for reducing the amount of power consumed by the electronic components, and using lower cost components, whenever possible.
Attempting to use lower cost components and reduce power consumption to keep meter costs down is relevant to any meter environment, and particularly the residential meter environment. For example, although the invention is not limited to this application alone, 240 VAC residential meters often use limited current, fixed voltage capability power supplies (e.g., a linear capacitive divider power supply), which apply even greater power constraints on the power supply.
Electronic meters often employ an optical communications port used to determine electrical usage, to read the meter, and/or to provide meter indicators and test features. In order to provide such data via the optical communications port, an optical diode is used. The optical diode or light emitting diode (LED) operates as a transducer to convert electrical energy provided to it by the other meter components to light or other optical signals. The optical signal is communicated with a communications port that provides the light external to the meter. In this way, an optical receiving device may be placed over the optical communications port to receive the data processed by the meter. In an electronic meter, the power required to operate the optical diode often is equal to or even more than the power required by the other electronic circuits combined.
Therefore, there is a need to reduce the amount of power consumed by an electronic meter, and particularly by the optical diode.